1. Field
The embodiments discussed herein are directed to an illumination device, a surface light source device and an illumination unit. An illumination device or a surface light source device in accordance with the present invention is applied to backlighting of LCD panel. An illumination unit comprises said devices and a member-to-be-illuminated such as LCD panel. The present invention is applicable to illumination devices and surface light source devices for backlighting in TV-monitor displays or personal computer's monitor displays. The present invention is also applicable to uses such as interior indication illumination or various illuminators.
2. Description of the Related Art
Surface light source devices or illumination devices employing a plurality of fluorescent lamps (linear light sources) have been conventionally used as illumination means for LCD monitors used in personal computers, television sets or the like. In general, a device of such kind is composed of a plate-like diffusion member, a reflection member and a plurality of fluorescent lamps (linear primary light sources) disposed between the diffusion member and the reflection member. The diffusion member and the reflection member has generally the same shape and size as those of a LCD panel of the LCD monitor.
Light of the fluorescent lamps is inputted to a light inputting face (i.e. a face directed to the reflection member) of the diffusion member directly or after being reflected by the reflection member, being diffused and then outputted from a light outputting face (i.e. a face opposite to the light inputting face).
Diffusion effected by the diffusion member causes the light outputting face to show brightness uniform to a certain extent. However, areas just above the respective fluorescent lamps and vicinage thereof (called primary-light-source-corresponding-area) are different in brightness from the other area (called primary-light-source-non-corresponding-area). In other words, the primary-light-source-non-corresponding-area gives a reduced brightness as compared with the primary-light-source-corresponding-area.
Document 1 (JP 2003-279978 A) provides a solution for overcoming such a problem. FIG. 17 illustrates the solution. Referring to FIG., light source device 100 comprises fluorescent lamps 101 diffusion member 102.
Thickness of diffusion member 102 is large at just above fluorescent lamp 101, 210 (namely, in the primary-light-source-corresponding-area) and small between fluorescent lamps 101, 101 adjacent to each other (namely, in the primary-light-source-non-corresponding-area).
This causes light outputted from the primary-light-source-corresponding-area to be more attenuated by absorption as compared with light outputted from the primary-light-source-non-corresponding-area. As a result, brightness increasing in primary-light-source-corresponding-area is suppressed, leading to a uniform brightness.
However, obtaining a uniform brightness tends to bring a much reduced light utilization efficiency because the art relies on partial absorption of light traveling toward the primary-light-source-corresponding-area. Doubtlessly, this is not desirable.